Pilot stem



Oct.- 15, 1940. c. T. RoTTLER PILOT STEM Filed Nov. 22, 193e Cla/amc@ Z" j? 0117er rig.I 4 Y nventor Gttorneg Patented Oct. 15, 1940 UNITED STATES PATENT@ OFFICE;

v y I Clarence T. Rottler, Seattle, Wash. Application November 22, 1938, Serial No. 241,764

i4 Claims.

The present invention relates to pilot stems for insertion in bores to serve as an axial guide means for an operation to be performed upon the bore or upon some surface which is, or which '5 isintended to be, coaxial with the bore. Such a device finds a particular application inthe reseating of the valve seat of an internal combustion engine, the pilot stem being brought into substantial axial coincidence with. theaxis of l the bore which normally receives and guides the valve stem, and then serving as a means to position or axially align a reseating or grinding tool relative to the valve seat.

Such pilot stems generically are old, but it has l5 been found diilicult heretofore to secure exact axial coincidence between the pilot stem and the bore, and if occasionally exact axial coincidence is obtained it is largely fort-uitous. The dilculty in insuring axial coincidence, with certain former constructions, is that it has been attempted to secure this by centering a rod at one point of engagement with the bore, hoping thereby to obtain substantial coincidence between the axis of the rod and of the bore. However, because the tight engagement of therod within the bore is at one point only, usually .at the entrance to the bore through the medium of a taper on the rod inserted within the entrance, this does not obtain axial coincidence, but merely centering of this particular circle of engagement; if there'is` any looseness between the rod and the bore at Yother points in the length of the rod, `as there must be in practice in order to permit insertion'of the rod through the bore, this looseness, though minute in amount, causes some tilt of the axis of the rod relative to the axis of the bore, and the entire valve grinding or reseating operation becomes inaccurate. While the actual deviation may be slight-and the measurements with which we are 40 dealing are 'of the order of thousandths or'tens of thousandths of an inch-nevertheless even a minute deviation from true axial coincidence, when magnied by `the greater diameter of the Valve seat, becomes of considerable practical importance.

Attempts have been made to remedy ythis diniculty by centering the inserted end of the rod, relative to the inner or distant end of the bore, by means operable independently of the taper at the entrance to the bore, for instance, by expansive devices at the distant ,end of the bore, but this has not proven entirely satisfactory, and in particular is in certain constructions attended with the difculty of having to reach inside the .engine to the lower endof the bore, and there in arestricted space to adjust a centeringmeans. l In other prior devices it has been attempted, by adjusting means extending through van axial bore in the stem to avoid the necessity of adjusting a lower centering device from within the 5 engine, or at the' lower end of the bore. Since the bore is of small'diameter and the stem must y be even smaller, a hole through the stems axis weakens the stem, and withal the adjusting device is still so small and frail that vit can not be 10 relied upon to accomplish the adjustment properly or accurately, nor to kstand up under 'rough treatment whichit is bound to receive when used by careless mechanics, men not thoroughlyskilled in the use of such tools. Such devices are there- 15 fore unsuitable, largely because of the necessarily small size of the operating parts, or the weakening of the r.stem itself if the operating parts are made larger.

To provide a larger operating element `to con- 20 trol the adjustment of a sleevel threaded on the inserted end'of a rod, without weakening the rod, it has been attempted to adjust thesleeve with relation to an expanding taper on the rod, by rotating therod itself, the sleeve being held 25 against rotation by frictional engagement with the wall of thebore. This will unquestionably eifect expansion `of the sleeve, and if the sleeve expands fully, and remains concentric vwith the rod, the'latter' will unquestionably be correctly 30 centered at this distant end, and aligned throughout its length, but still such devices have been found impracticalv in use. The mechanic only knows'that he must rotate the projecting end of the stem to expand and tighten the sleeve, and does not realize that he can.` expand the sleeve too greatly, even before its frictional grip is sufficient to prevent further rotation of the rod.` He turns the rod,` and continues to turn it, perhaps believing that the sleeve is slipping or rotating within the bore, and knowing that the top taper is resisting rotation of therod, and

so greatly expands the sleeve that it breaks, or

expands it to a point where it willnot again contract to its original diameterfor shapeit bev45 cornes permanently deformed and is not longer accurate. He continues to turn the rod until the sleeve does nally grip and refuse to turn farther, and then he tries `to turn the rod a little farther to insurethat it is tight. lIn thus turning -50 the rod against resistance (whether of the top taper or of the expanded sleeve) he strains it, and bends or breaks it. Y The-.difficulty is that he has no way of telling when thestem as a whole is centered, and there is nothing to prevent turnl ing the rod too far. Force must be exerted on the rod to tighten the expanding sleeve, and since insufficient force leaves the sleeve loose, eX- cessive force will usually be employed, and such force injures the stem and destroys its accuracy.

On the other hand, the top taper is so slight that it wedges easily, and resists rotation of the rod, before the rod has turned sufficiently to expand the sleeve to the desired degree. By this wedging of the -top taper, as it rotates, the rod may be engagedtightly enough 'that' it will not turn farther, tightly enough that the engine block may be lifted by the wedged rod-yet, if it becomes so wedged after one turn, and three kturns are necessary to effect sufficient expansion of the' sleeve on the lower taper, it is self-evidentthat the sleeve is loose within the bore a lack of expansion equivalent to two 'turns. If-the lsleeve is left thus loose-and if the rod can not .be

turned farther the average mechanic is justified in believing that the sleeve mnstbetight--it can not perfectly center therod, ,andplack of axial coincidence results. Itv is` essential, if the rod must be rotated, that thefsleevefs expansion be not dependent, vin degree-upon .the amount of rotation of the rod, .but that the sleeves .expansion befully accomplished by means which operate independently `of .the `rods rotation, though such means may be .trippedor set in operation by rotation of the rod. l

It is the principal object` of this invention to provide a pilot stem for such uses, which is so constructed as to automatically-secure. substantially exact axial coincidence between the axis of the rod andthe axis. ofthebore, by reason of two automatic centering devices'in the nature of tapers acting upon two circles-or. zones, spaced well apart toward opposite ends of the bore, to the end of reducing the possibility oflack of coincidence to the minimum, .and` asa .subsidiary object it is a further objectxto effect thiscoincidence by means whichare operable: wholly exteriorly of the bore', and'. from the projecting end of the rod, and exerting automatically. aV force sufficient to effect proper centering,fbutvunlikely-to have applied to it any excessive; forca-since-the centering of the lower end is automatic, and the user knows when the .latter occurs, and needs only center the upper taper... 4 u

A further diiculty with former devices ,has been that the centering of a particular portion of the `rod (the distant or inner end', usually) has been eiected almost solely byilinecontactabout a circle, such as the Ycontact of ataper with the edge constituting one or the `other end of the bore, and since such edgeorline contact may be rendered inaccurate by inacc-uracy'of the edge itself, orby slight unnoticea-ble 4deformation of one or the other'of theI contacting surfaces or edges, it is `a further object to effect this axial coincidence, in lpart Aat least, V.bywengagernent throughout a zone of appreciable length of the bore, thus to avoid inaccuracy due to line contact.

It has also been proposed to effect centering, usually at the inserted end iithe rod, by an exp'ansible sleeve 'slit throughout its length, and expanded by screwing it along the rod against an expanding taper.-" yWhile this sleevemay be coaxial Vwith the `rod when collapsed; when expanded by separation of the "edges lof., the slit it loses, even though by a small amount, true' axial coincidence, which thro-ws therod off, and it is no longer truly-cylindrical, -lfiencev bears along a `linelor 'lines ir'iste'adI of over a cylindrical surface, thereby increasing' thepossibility of failure to retain axial coincidence, statically or under stress. A further object of thisinvention is to provide a structure which will eliminate these possibilities of error.

It is a further object to provide a pilot stem of the character indicated, automatically and simply self-centering, under control of the user, when inserted, which is simple and rugged in construction, made of few parts, operable with a minimum cf effort, andA capable, in all parts where, this is necessary, of precision manufacture, all to the ultimate end that there shall be provided a pilot stem which with unfailing accuracy will at all times align itself axially with the axis of the bore, and will pro-vide an unfailingly accurate guide for further operations, such as the grinding or reseating of a valve seat.

To the above ends my invention comprises the novel pilot stem as a whole, and the novel come bination and arrangement of the elements thereof, as shown in the accompanying drawing, described in this specification, and as will be more particularly defined `by the claims which terminate the same.

In the accompanying drawing I have shown my invention embodied in a form which is at present preferred by me, it being understood, however, that the principles of this invention, in accordance with the appendedy claims, may be incorporated in other forms and arrangements,

and this specification, while directed to Aa specific form, is to be understood as, explanatory rather than as restrictive.

Figure 1 is a general-elevation of the pilot :stem

and .an associated valve seating tool, shown in operative position, the bore, valve seat, and associated parts being shown in section.

Figure 2 is an enlarged elevation of the stem, with parts vin. section, and in the positions they occupy in Figure 1.

Figure 3 isa further enlargement yof the inner or inserted end of the stem, showing parts in the position they would occupy during, insertion.

Figure -4 is a top plan, view of the sleeve which forms. part ofthe stem, land which constitutes its inner centering and bearing member.

The particular type of tool with which the stem cooperates is per se immaterial, but in order to afford an understanding of the stem and of the reason why it must be so accurately located,

tool comprises a body 9 having a .conical 'surface g 9D which is shaped to seat upon a perfectly shaped valve seat 80, in an engine block 8, the tool being l provided with ya cutting bit 9|l which is intended to be projected from the conical surface .gil to a minute extent (the .adjustment being regulated by a threadedly` mounted adjusting element 452), so that as the `tool is rotated, axially aligned with the axis of the seat Si), itwill in effect seat throughout its entire periphery by engagement of the conical surface 90 with the conical seat 80, and the tool- 9| will project only to an extent to remove the high surfaces or points of the valve seat, but -insuiciently to raise the conical surfaces 99 and 8l)v from substantially fu-Il contact with each other. by the contact of the two conical surfaces mentioned, yet still it must be centered relative to the axis of the valve seat, and this centering is accomplished by a rod I, which forms part of the pilot stem, this rod having a portion 4which pro- This tool is guided largely 1eft,'fo'r instance, asseen in-Figure 1,"then--by ,-ifzthe axis of the-rod I be noniiig'supstanuauy precisecoincidence with the axis of the valve Seat 89, but fif it be instead'tlted Slightly, tolfth'e reason ofthe enlarged diameterof theA valve seat,

' the tool 9| willV out more deeplyl at "the leftin Figure l, and more lightly attheright, withl the result that Athe'valve seat becomes tilted with respect to the surface 8|, and therefore somewhat -tion to the spring.l

elliptical, and the valve, when replaced,'does not seat accurately.. Moreover, more work is required since more material-'must be removed to make the seat elliptical, and the nal result is 'that 'the 'valve does not seat accurately and the engine does not function efficiently. Other'disadvan tages arise fromsuch an imperfectly' aligned rod, but enough has been said to'indicate why precise alignment must be obtained if possible." It may be assumed that the bore 82, within which the stem of the valve lis received, is accurately and precisely aligned Vwith the axis of vthe valve seat 8U, for originallylthe valve seat was so located by reference tothe bore.l The axisof this bore 82 may therefore beitaken as the reference line from which all otherdeterminations are made, but it is useless as a reference line unless 4the axis of the stemI may unfailingly be brought into precise axial coincidence with the axis of the bore, and itis at devicesv have failed.

The stern` I may be caused to seat at theen" trance to the bore 82, which would normally be its upper end, and to center itself in the ,circle which defines this entrance by providing va'taper II, intermediate the ends ofthe rod I, which is of asize and shape to seat in the entrance to the bore. .This, ,however, only fcenter's the circle of Contact between thetaper II andthe entrance 4to theubore, andudoes not,`of itself, insure axial coincidence between lthe bore and the rod. Since axial coincidence can bestbe assured by two accuratebearings, spacedas farapart as is fea- -sible, I provide selfTcentering means which will engage the Vdistant,usually the lower, end ofthe bore 82, and whichwill center this end of the rod,

-and thereby, by cooperation with the centering afforded bythe taper I I will'effect substantial axial coincidence between the, rod andthe bore.

The means to theilatterA end may vary. somewhat. Ineffect they are ,constituted by a plurality of radially and equally movable wedging or gripping elements, togethenwith means, preferably operable from the projecting or upper end vof the rod, and under the limited yet suioient' force of aspring'; to effect their-radial expansion; preferablyvalso in much the sameway their retraction is -eieoted' though, of course, in opposijl Thus adjacent'the inner or inserted end of the`rod I I provide asecond taper I 2, which should taper in thefs'a'me -direction-as'the taper I I. The two need not be' parallelgbut tend ltoward par allelis'm,v both being inclined' in they same L direction 'miam/'eroine axis ofthe rod. In'this connection, and, generally in connection with. the description o-fthisV pilot stem, it must be borne in this point that'prior This"A sleeve is slit lengthwise -at'v spaced points from' its' top` downwardly forapart llol its length, but preferably the slits 2o do not extend theen.- tire length of the sleeve, leaving anv unslit portion at its lower end', which is closelyfguided upon the reduced portion I3 of the rod. This leaves longitudinally extendingl fingers 2|,.which are somewhat resilient so-that they maylbe moved outwardly when the f sleeve. as va whole is moved lengthwise of` the rod into,` engagement or into more rm-engagementwwith', the taper I2."The inside of Vtleflngers 2| may be complementally `:taperedfi'io engage the taper I2, i'f'desired, and preferably in thevv vicinity of their taper-engaging portion they are exteriorly formed cylindrically, as lindic'zated at 22, to effect a bearing or gripping engagement throughout' an appreciable portion ofthe length of the bore 82, thus 'to avoid mere une Contact with the wan ofthe bore.

Norma1ly,'that is, Afor insertion of the stern, the

ngers 2'I and their gripping portions '22 are-retained in a position `where they are collapsed,that

is, where they are expanded radially outward to the least degree, yet still they should be of suicient-diametrical extent' that they ifrictionally engage Athe"wall'of the bore-82,l It is'further de'- sirable, afterf'the stemf is `rinserted andthe first taper I Iis well seated in theentrance to thev bore, 'thatV the wedging elements 2|, 2 2 should be radially and equallyeXpanded-'in all directions,

and by @-a'predetermined force which tends to p ullithe rod I further into the bore 8,2,l thus to seat the taper I'Imore securely in the'entrance Thelatter ends are secured, in the construction Vs l'iown-,by providing a head 3, which is riveted or Aotherwise permanently* secured on the end of the rod, by providing an expansion spring 4 reacting between the head Sand-the lower'end of the sleeve 2, and j'by restraining the sleeve against theactio'n of they spring I4 by a retaining means yshown ,as lformed of a pin 4I4 projecting laterally fromfthe rod and received within an angled slot in jtheysleeve 2, and vindicated generally at 24.

not tobe implied that the upper end of the sleeve Vmust not v,touch the taper I2, even though so shown in Figure v3, but it must vnot press against the taper I2 sufficiently to expand the upper ends ofthefmgers 27| into gripping engagement with the wall'of thebore. However, when, by rotation of therod I `relative' tothe s1eeve'2, the piny I4 has been brought into registry with that branch ofthe slot 2 4v `which ext'ends' 1engthwise of the sleeve, thesleeve, under the impulse of the compressed spring 4, is moved or thrust upwardly, and lay-reaction the rod I is pulled downwardly or inf wardly, and now, as the free ends ofthe fingers taper -I 2, the fingers are moved or pressedradially outwardly, increasing the frictional grip of the cylindrical outer surfaces of the gripping Vportion 22 upon the wall of the bore, and wedging be- -tweenthe taper I2. and thewall Vof the bore, to

effect ,centeringoff this lower ,or inserted 1endof v2| ride up on or engage more rmly with the iBU cidence of the rods axis at each of two rather widely spaced points, it follows that there must result substantially exact axial coincidence between thev rod I and the bore 82. e

i It has been stated above that the sleeve, vat least its portion 22, when in the position of parts shown in Figure 3, frictionally engages the wall of the bore 82;` This need not be too close fric- `tional engagement, but must be suiicient. that when -the upper or projecting end of the rod is rotated v(as, for instance, by a cross pin received inthe transverse hole I5), the sleeve 2 will not rotate, thereby permitting the pin I4 to move into registry with the lengthwise branch of the angled slot 24, and as soon as these are brought into registry, lengthwise movement of the sleeve 2 relative to the rod I is accomplished, under the iniiuence of the spring 4, thereby tremendously increasing the frictional grip of the elements 22.

.Thus the stem as a whole may be inserted into the upper or near end of the bore 82, until its taper II is seated at the entrance to the bore,

and then ,by rotation of the projecting end of the rod the sleeve is brought into wedging orgripping engagement with the distant or inner end of the bore, in the manner just described. When it is desired to remove the pilot stem it is.only necessary to pull upwardly on the rod I, again .compressing the spring 4, rotating the rod I in the opposite direction tomove the pin I4 intothe peripherally directed branch of the slot 24, whereupon, with the ngers 2 I, 22 again retracted byhtheir natural resilience, the stem as a whole may be lifted out of the bore.

What I claim as my invention is:

l. A vpilot stem for reception in a guide bore, comprising a rod formed intermediate its ends to seat on and to center itself relative to the near end of the bore, a normally collapsed but resiliently expansible sleeve which in all positions is coaxial with and guided upon the distant end of the rod for movement relative` to the rod, means to retain .said sleeve in a position wherein it is collapsed, the sleeve when thus collapsed being of a size to vfrictionally engage the walls of the bore, means operable by movement of the rod relativeto-the frictionally engaged sleeve, when each is thus engaged, within the bore, to release said, retaining means, and means operable as a result "of such release to effect expansion of the sleeve into gripping and self-centering engagement with the bore, thereby centering the distant end of the rod with the bore, and aligning the rod as a whole coaxially with the bore.A

2.,A pilot steinfor reception in a guide bore, comprising a rod formed intermediate its ends to seat on and to center itself` relative to the neark end of the bore, an expansible sleeve which in all positions is coaxial with and guided upon the distant or inserted end of the rod for movement Aaxially along the rod, means operable by --movement of the sleeve towards the yrods seating portion to expandv the. sleeve radially into vgripping engagement with the wall of the bore, thereby, injcooperationfwith the seating portion, to

eiect substantialpoincidence betweenrthe axes to seat on and to center itself relative to the near end v of the bore, an expansible sleeve which inl all posi-tionsis coaxial with and guided upon thedistantorlinserted end of the rod for movement axially. ,along the rod, means operable by movement of the sleeve. towards the rods seating portions to expand the sleeve radially into gripping engagement with the wall of the bore, thereby, in cooperation withthe seating portion, to effect substantial coincidence between the axes of the rod and bore, means active'to eiTect such movement ofthe sleeve, and means, releasable by rotary movement ,in yone direction of the projecting endof the rod relative to the sleeve to permit such movement, operable to restrain the sleeve Aagainst such vmovement during insertion i' of the 'rodand reengageable by rotary movement in the oppositedirection of the rod relative to the sleeve, to enable collapse of -the sleeve during withdrawal of the rod.

4.",A pilot stemior reception in a guide bore, I

comprisingca rodtapered intermediate its ends to seat on and to center itself relative to the near end of the bore, a normally collapsed but resiliently expansiblesleeve in all positions-coaxial with and guided `upon ,the ,distant ,end of the rod for movementlengthwse ofjthe rod, means toretainsaid sleevein a position .wherein it is Vcollapsed, the sleeve ,when thus collapsed being of a s ize 4to `frictionally engageY the walls of the bore, and means operable bytlimited movement of the rod4 relative to the frictionally-engaged sleeve," when each yis thus engaged within the bore, to 4'release said retainingmeans and to eie'ct immediate expansion ofthe sleeve into gripping and self-centering engagement with the bore, and coincident movementjof the sleeve lengthwise of the rod and towards its taper, thereby centering the twoends `of the'rod with the bore, and locating therod asa' rwhole coaxiallywith the bore.

5. A pilot Istem for reception in a guide bore, comprising va rod tapered vintermediate its ends to 'seat on andto `center itself relative to the near endof the bore, a sleeve having a'non-expansible portion'closelyembracing the distant inserted end of the rodto guide 'the sleeve for movement dially` -expansible portion ora size and shape,

when not expanded, 'to frictionally engage the innerwall of the bore, means to urge the sleeve along the rod in -a direction towards the rods taper, the rod and sleeve havingcomplemental means operable by movement ofthe sleeve towards the rodstaper toexpand. the sleeve into gripping engagement fwith the wall of the bore, and the sleeve being externally shaped to engage, whenexpanded, van lappreciable portion of the length of the bore, thereby to center the sleeve and the corresponding end of the rod within the bore, and todrawl the taper firmly into the entrance to the bore, thereby, in conjunction with the aforesaid 'centeringactiom to effect substantial coincidence between the axes of the bore and rod, and means, releasable from the projecting end of lthe -rod, -Jto retain -the'sleeve in a position wherein 'it' 'is Icollapsed.

-f G-fA; pizlotfstemifer reception-ina einde bore,

eomprisiesa rodhavine a rsti taper irlterrfleden ?.ts-endsfie 1a Size -andgshapefto sat nthe entrar-rcev to-v the bore,and to center itself and the intermediate part of the rod relative to such entranceptherod alsohaving a second taper, in the same direction, adjacent its distant or inserted end, wedging elementsv distributed about the rods inserted end inwardly of the second taper, and engageable with the second taper, when' moved towards the same, to be thereby expanded radially and equally into gripping engagement with the bores wall, to center this inserted end of the rod with the bore, and hence, in cooperation with the rst taper, to eect substantial coincidence between the axes ofthe rod and bore, means urging said wedging elements towards wedging position; and means acting inl opposition to the latter means, and releasable from the projecting end of the rod, to retain said wedging elements in non-wedging position, thereby to withhold them from such radial expansion during insertion of the rod.

7. A pilot stem for insertion within a guide bore, comprising a rod having a rst taper intermediate its ends, of a size and shape to seat on the entrance to the bore, and to center itself and the intermediate part of the rod relative to such entrance, a head formed on the rod at its distant or inserted end, the rod also having a second taper, in the same direction as the irst, adjacent the head but between the head and the first taper, wedging elements distributed about the rod, between the head and the second taper, and engageable with the second taper, when moved towards the same, to be thereby moved radially and equally into wedging engagement between the second taper and the bores wall, to center this inserted end of the rod within the bore, and hence, in cooperation with the first taper, to effect substantial coincidence between the axes of the rod and bore, means releasable from the projecting end of the rod to retain said wedging elements withdrawn towards the head, `thereby to withhold them from such engagement with the second taper during insertion of the rod, and spring means reacting, lengthwise of the rod, between the head and the wedging elements, whereby upon release of said retaining means, to simultaneously urge the first taper into the entrance to the bore, and to thrust the wedging elements towards the bores entrance into operative engagement with the second taper.

8. A pilot stem as in claim 7, including a sleeve coaxial with and slidable lengthwise of the inserted end of the rod, and having lengthwise slits spaced about its periphery, for a part only of its length, to constitute the Wedging elements, the spring means reacting between the head and the unslit portion of said sleeve.

9. A pilot stem as in claim '7, including a sleeve A'coaxial with and slidable lengthwise of the inserted end of the rod, and having lengthwise urging of the spring means when, by rotation oftherrod relative to ,the ,sleeve the pin Comes into K registry witl i s aid lengthwise .branch of meant-,l i; lll-:The ombmaiion. Qf-,Qlalm 6, wherein the wedging elenntsarejiormed by slittingL .a Sleeve nwldly pffQmQLnenq; only, :a-fangllllr 1V Spafed points,` and for a rportion only'of its length, to define a plurality of substantially identical wallengaging ngers resiliently supported from an integral unslit skirt, and wherein the retaining means is in part formed as part of said skirt, and in part upon the rod.

11. A pilot stem for insertion Within a guide bore, comprisinga solid rod of a transverse s ectional area approaching the transverse'area of such guide bore, an expansible sleeve encircling the insertible end of said rod, means permanently securing together said rod and said sleeve and restraining them from substantial relative rotative movement, and means operable by relative axial, non-rotative movement of said rod and` sleeve in one direction to eiTect expansion of said sleeve into rm gripping engagement with the wall of the guide bore, and releasable by relative axial, nonrotative movement in-the opposite direction for contraction of said sleeve.

12. A pilot' stem for insertion within a guide bore, comprising a solid rod of a transverse sectional area approaching the transverse area of such guide bore, an expansible sleeve encircling the insertible end of said rod, means permanently securing together said rod and said sleeve and A restraining them from substantial relative rotative movement, means operable by relative axial, non-rotative movement of said rod and sleeve in one direction to effect expansion of said sleeve into rm gripping engagement with the wall of the guide bore, and releasable by relative axial, non-rotative movement in the opposite direction for contraction of said sleeve, and means cooperable with said rst means by slight relative rotation of said rod and said sleeve to restrain such rod and sleeve from appreciable relative axial movement, thereby to lock said second means against sleeve-expanding movement.

13. A pilot stem for insertion within a guide bore, comprising a rod having means intermediate its ends to center such intermediate portion within the entrance to the bore, an expansible annulus carried by the inserted end of said rod and provided with a wedging surface, cooperat- 4ing wedging means movable with respect to the wedging surface of said annulus to expand it into gripping engagement with the wall of the guide bore, spring means acting to urge said wedging means and wedging surface into engagement to effect gripping expansion of said annulus, and spring control means operable to render said spring means inactive and incapable ofv effecting annulus expansion, and releasable to render said spring means again active to effect expansion of said annulus into gripping engagement with the wall of the guide bore.

14. A pilot stem for insertion within a guide bore, comprising a rod having means intermediate its ends to center such intermediateportion within the entrance to the bore, an expansible annulus carried by the inserted end of said rod for engagement with the wall of the guide bore, and provided with an annular wedging surface,

cooperating wedging means movable axially relative to said annular wedging surface, a compression spring expansible axially of said annular wedging surface to force it and Vsaid wedging means together to expand said annulus into gripping engagement with the wall of the guide bore, and spring control means operable from the end of the rod projecting outwardly from said rst means to compress said spring and to retain it compressed for releasing said annulus from such wall gripping engagement, and further operable from such projecting end of the rod to release said spring for expansion to force said wedgng means and Wedglng surface together for expanding said annulus into suclg wall gripping engagement.

CLARENCE T. RO'II'LER. 

